Organo-tin hydrides, especially tri-n-butyl-tin hydride, are valuable organic-synthesis reagents with an extraordinarily wide range of applications. These compounds are highly selective reducing agents Furthermore, the organo-tin hydrides may be used, for example, as catalyst, stabilizers, or biocides. The value and importance of these compounds has been demonstrated in a number of publications. Detailed information can be obtained from such reviews as W. P. Neumann, Synthesis 1987, 655; B. Giese, Radicals in Organic Synthesis: Formation of Carbon Bonds, Oxford, Pergamon Press, 1986; M. Pereyre, J. P. Quintard, & A. Rahm, Tin in Organic Synthesis, London, Butterworth, 1987; D. P. Curran, Synthesis 1988, 417 & 489; I. Omar, Organotin Chemistry, Amsterdam, Elsevier, 1989; and P. G. Harrison, Chemistry of Tin, Glasgow & London, Blackie, 1989.
Despite the wide range of applications reported in the prior art for these compounds, industrial use has been restricted by the limited stability of the organo-tin hydrides, which subsequently is a direct result of unsatisfactory preparation and purification techniques employed in prior art processes.
The instability of the organo-tin hydrides is caused by trace quantities of contaminants that remain in the product even after separation and extraction. Such trace amounts of contaminants are known to hinder the production of the hydrides and/or directly catalyze their decomposition. For example, traces of Lewis acids such as aluminum, boron, and organo-aluminum and organo-tin halogenides are known to trigger immediate decomposition of the resultant organo-tin hydride compound.
Some methods of stabilizing these organo-tin hydrides subsequently have been published. Such methods are disclosed, for example, in German Patent No. 1 167 345 & German, Patent No. 1 468 709. These references disclose purification of the organo-tin hydride compound by additional extraction with alcohols or basic solutions. However, this additional extraction method is inefficient and results in unacceptably low yields of product.
Other methods of preparing organo-tin hydrides have also been described in the prior art, however, these methods contain the above-mentioned drawbacks and/or result in low yields of the organo-tin hydrides. These methods of preparing organo-tin hydrides are illustrated hereinbelow.
U.S. Pat. No. 4,282,166 describes a method of preparing trialkyl-tin hydrides from trialkyl-tin chloride and sodium bis-(2-alkoxyethoxy) aluminum dihydride.
Chemical Abstract No. 90: 204 205p describes reducing trialkyl-tin chloride with sodium borohydride (NaBH.sub.4) in mixtures of ether and water. Yields of about 65 to 80% are obtained by employing this particular method.
U.S. Pat. No. 3,439,010 describes obtaining yields of approximately 80% trialkyl-tin hydrides by thermally decomposing trialkyl-tin formiates.
The preparation of organo-tin hydrides from sodium hydride and alkyl-tin chlorides is described in U.S. Pat. No. 3,401,183.
Alkyl-tin oxides and chlorides can be converted into tin hydrides with siloxanes and silanes. This process is described in the following references: K. Hayashi, et al., J. Organomet. Chem. 10, 1, 81-94; Japanese Patent 43 010 134 [Chemical Abstr. No. 69: 106 880 b]; Japanese Patent 43 010 133 [Chemical Abstr. No. 69: 106 879 h]; Japanese Patent 43 012 132 [Chemical Abstr. No. 70: 37 922 y]; and German Patent 3 119 643.
H. J. Albert, T. N. Mitchell, and W. P. Neumann in H. Zimmer, ed., Methodicum Chimicum Vol. 7, Part A, New York, Academic Press, 1977, 361-62 describes the use of aluminum lithium hydride (LiAlH.sub.4) which subsequently yields 66 to about 89% trialkyl-tin hydrides.
Satisfactory yields can be obtained by reacting trialkyl-tin chlorides with sodium borohydride, although the reaction and preparation are complicated and difficult. This particular reaction is described in J. Organomet. Chem. 9, 2, 379-82 (1967).
Hungarian Patent A-41-412 describes a method of preparing tri-n-butyl-tin-hydride from bis-[tri-n-butyl-tin]oxide. The process is characterized by dissolving the oxide in an aliphatic alcohol and reacting the mixture at 10.degree. to 30.degree. C. with an alcoholic and/or aqueous solution of sodium borohydride for 10 to 60 minutes. Yields of 64 to 84% tri-n-butyl-tin hydride are isolated subsequent to a complicated series of purifications.
Despite the numerous methods available in the art, continual research is ongoing in an attempt to provide an easier method of preparing organo-tin hydrides which are stable under normal storage conditions over a longer period of time.